1. Field of the Invention
This invention generally relates to signal communications and, more particularly, to a system and method that uses the preamble of a multichannel Optical Transport Network (OTN) protocol signal to calibrate for skew errors.
2. Description of the Related Art
100 gigabit per second (Gbps) OTN protocols are being developed where the OTN streams are carried in a “parallel fashion” at a bit-rate greater than 100 Gbps. Until recently, optical signals have been carried using modulations techniques carrying 1 bit per symbol. However, the need for faster signal speeds means that return to zero (RZ), non-return to zero (NRZ), and phase-shift keying (PSK) modulation techniques (1 bit per symbol) are no longer suitable.
FIG. 1 is a schematic diagram depicting a system for the transmission of high speed signals (40/100 Gbps and above) using multiplexed orthogonal optical polarization, with 2 bits per symbol per polarization, for a total of 4 bits/symbol. Any skew (differential time delay) experienced in the modulation of the transmitted signal is translated to the receiver, making the recovery of a serial stream from parallel streams difficult.
It would be advantageous if a technique could be developed to minimize differential time delay or skew in the parallel pathways of a multiplexed orthogonally polarized OTN signal.